Hot electrons at metal-organic interface: Time-resolved two-photon photoemission study of phenol on Ag(111)

Abstract

<jats:p>We used time-resolved two-photon photoemission (2PPE) spectroscopy to investigate the excitation mechanism and dynamical behavior of the anionic molecular resonance (MR) state of phenol weakly interacting with Ag(111). The photoexcited MR state of phenol was found at 3.1 eV above the Fermi level at 1 ML (monolayer) coverage, and the binding energy of this state remained rather constant at 0.74±0.05eV for all coverages. The polarization angle dependence of the 2PPE signal clearly showed that the MR state is populated by an indirect excitation process involving scattering of photoexcited hot electrons rather than direct electronic transition from a bulk band. The lifetime of the MR state was found to increase from 33 to 60 fs upon increasing the coverage from 1 to 9 ML, implying that the MR state becomes further decoupled from the bulk at a higher coverage. These results constitute the first time-resolved 2PPE study that clearly demonstrates the hot-electron-mediated mechanism operating for molecules that are potentially active photochemically but weakly interacting with a metal surface.</jats:p>